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    <meta charset="UTF-8">
    <title>变量</title>
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<script>

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    var obj2=undefined;
    var obj3;
    document.write("1"+"~~~"+typeof obj1+"<br>")
    document.write("2"+"~~~"+typeof obj2+"<br>")
    document.write("3"+"~~~"+typeof obj3+"<br>")

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